Thermoplastic Adhesive Research Articles

Press Conduction Welding for Secondary Bonding of Aircraft Skin/Stiffener Assemblies Using Carbon Fiber/PEKK Thermoplastic Composites and PEI Adhesive.

This study investigates the secondary bonding of aircraft skin/stiffener assemblies using press conduction welding with carbon fiber/polyetherketoneketone thermoplastic composites and polyetherimide adhesive. Recognizing the challenges posed by conventional welding methods in maintaining material integrity and uniformity, this research explores an alternative methodology that mitigates these issues while ensuring high-strength bonds. The press conduction welding parameters were selected based on single-lap shear tests and applied in the bonding of skin and omega stiffener components. The temperature range was determined using differential scanning calorimetry. The pressure was held at 1 MPa for 180 s. The welding temperature that produced a high-bonding strength was identified experimentally; these key variables were then used in the welding process of the skin and omega stiffener. By analyzing how the fibers tear and the effectiveness of interdiffusion between the plies, we were able to gain insights into the bonding strength and fractured surface. The findings suggest that press conduction welding provides a viable route for secondary bonding in thermoplastic composite structures, highlighting its advantages in terms of processing efficiency and integrity. This study contributes to the understanding of the mechanical behaviors of bonded joints and underscores the significance of temperature control in the welding process.

In-situ aligning magnetic nanoparticles in thermoplastic adhesives for contactless rapid joining of composite structures

Magnetic nanoparticles of high magnetic susceptibility, such as magnetite (Fe3O4), have been used for wireless heating of adhesives and composites through the magnetic hysteresis loss mechanism, but the high concentrations of nanoparticles needed to meet heating performance targets can degrade mechanical properties. Herein, we present an in-situ aligning method to enhance the heating efficiency of magnetite nanoparticles in a nylon thermoplastic matrix without adversely affecting its mechanical strength. A composite adhesive was made by dispersing Fe3O4 nanoparticles in a nylon matrix followed by hot melting. Experimental results show that by subjecting the adhesive to an alternating magnetic field during the hot-melt process, its heating rate can be improved by 200% compared to that without applying the magnetic field. The improvement in the heating performance has been identified to stem from the alignment of the ease axis of the magnetic nanoparticles. This in-situ aligning technique enables better induction heating performance with the same amount of Fe3O4 nanoparticles, avoiding the agglomeration problem of high nanoparticle concentrations. Moreover, this technique makes it possible to develop high-performance self-heating thermoplastic adhesive for reversible bonding and self-healing solution with a wide range of applications, such as bonding and debonding of composites, temporary attachment of systems, and recyclable bonded structures.

A renewable lignin-based thermoplastic adhesive for steel joining

Adhesive bonding of metals has become increasingly relevant in recent years due to the demand for reducing weight and improving performance in structural applications such as automobiles and aerospace. We developed renewable thermoplastic adhesives from technical organosolv lignin isolated from hardwood biomass and acrylonitrile butadiene co-polymer rubber (NBR) for joining steel substrates. NBR33, NBR41 and NBR51 with acrylonitrile molar ratios of 33, 41 and 51%, respectively, were blended with lignin to form two-phase thermoplastic adhesives, and their adhesion, viscoelastic and surface properties were measured. Lignin content in the compositions were varied, ranging from 40% to 80% (w/w), to alter toughness, stiffness, and surface energy characteristics of the material. Better interaction or reactivity between the lignin and NBR phases was observed with greater nitrile content in NBR, leading to greater modulus and stiffness of the adhesive. Simultaneously, increasing the proportion of lignin reduced toughness and improved stiffness, with the highest adhesive strength of 13.1 MPa measured in a 60% lignin loading ratio with NBR51. Surface energy measurements revealed that total surface energy (sum of polar and dispersive surface energy) raised with lignin loading, suggesting that both surface energy and matrix strength play a critical role in the adhesive properties of the synthesized materials. A finite element-based cohesive zone model (CZM) was developed and implemented to study the failure strength of the adhesively bonded joint. This study demonstrates the viability of lignin as a valuable building block for adhesives, not only due to its inherent chemical structure and rigidity, but also for its surface energy characteristics.

Towards Tough Thermoplastic Adhesive Tape by Microstructuring the Tape Using Tailored Defects

This paper presents a strategy towards achieving thermoplastic adhesive tapes with high toughness by microstructuring conventional tapes using tailored defects. Toughened tape was manufactured using two layers of a conventional tape where the bondline between the two adhesive layers was microstructured by embedding tailored defects with specific size and gap between them using PTFE film. Mode I toughness of the toughened tape was characterized experimentally. A high-fidelity finite element model was implemented to describe the toughening mechanisms using double cantilever beam simulations and end notch flexural tests. The model considers for the plasticity of the adhesive layer, the decohesion at the adherend-adhesive and adhesive-adhesive interfaces and progressive damage inside the adhesive layer. The adhesive-adhesive interface with the tailored defects inside the adhesive layer enables crack migration between adherend-adhesive interfaces, crack propagation at adhesive-adhesive interface, backward crack propagation under the defect, and plastic deformation of the adhesive ligament. The maximum toughness improvement of the tape with tailored defects of equal width and gap between two successive defects of 2 mm reached 278% and 147% for mode I and II, respectively, compared to conventional tape.

Modern thermoplastic (hot glue) versus organic-based adhesives and haft bond failure rate in experimental prehistoric ballistics

The prehistoric production of composite technologies throughout human evolution was facilitated greatly by the use of adhesives. One such technology was projectile weaponry, which used adhesive to attach a stone point to a wooden shaft. Prehistoric projectile weaponry is often studied via experimental archaeology, which recreates ancient technologies to understand their manufacture and function. Here, we explore whether a modern thermoplastic adhesive can serve as a suitable replacement for two organic adhesives that would have been used by past peoples – pine rosin and hide glue – in modern experimental tests of prehistoric weaponry. We conducted a ballistics experiment and shot groups of stone-tipped arrows, each group hafted with one of the three adhesives, and assessed the haft bond failure rate. The modern thermoplastic adhesive was similar to that of the pine rosin and significantly failed less often than the hide glue. We conclude that in some cases modern thermoplastic adhesive can be substituted for organic-based adhesives in experimental archaeology. Our results also show that hafting bond failure rate was significantly different between the pine rosin and the hide glue, suggesting that prehistoric hunter-gatherers faced costs or benefits in selecting adhesives for hafting.

Thermomechanical characterization of Nano-Fe3O4 reinforced thermoplastic adhesives and single lap-joints

In this work, Acrylonitrile Butadiene Styrene (ABS) was selected as the thermoplastic adhesive and reinforced with varying concentration of ferromagnetic nanoparticles (FMNP) through melt processing. The effect of FMNP content on thermo-mechanical properties was experimentally characterized. Also, lap-joints using glass-fiber substrates were bonded using ABS/FMNP films through conventional oven-bonding and induction-bonding techniques, and their effect on resulting joint behavior was studied. Further, effects of adhesive melt-processing mix-times and O2-plasma surface treatment on resulting joints were also studied. Results indicate that the percolation limit of FMNP to ensure melting and flow during induction bonding was 8 wt%, and the flow time decreased with increase in FMNP content. ABS adhesive with 16 wt % FMNP showed good balance of stiffness and strength relative to other concentrations. Both oven and induction bonded joints that were O2 - plasma treated had higher ductility relative to untreated joints. Further, induction bonded joints with both O2 -plasma and substrate preheating had 15% higher peak loads relative to oven-bonded joints. Optimization of the induction heating process parameters along with surface functionalization of particles and substrates is essential to fully exploit the benefits offered by these novel thermoplastic adhesives.

Influence of collagen modifications on qualitative parameters of thermoplastic adhesive mixtures and its microbiological stability

Influence of collagen modifications on qualitative parameters of thermoplastic adhesive mixtures and its microbiological stability.This work presents the possibility to use the modified biopolymer collagen for preparation of ecologic, biologically degradable thermoplastic adhesives. Collagen prepared from secondary raw materials of the leather and food industry was applied as a starting material for the preparation of thermoplastic, formaldehyde-free adhesives intended for use in woodworking, furniture and paper industries. Glued joint obtained high strength and flexibility after application of modification plasticisation agents based on collagen. Modifications of collagen glue with keratin biopolymer increased its resistance to water and the strength of the glued joint. Prepared samples of hot-melt adhesive had higher bonding strengths than standard commercial adhesives. The highest tensile strengths were achieved by applying of undiluted adhesive with the application of 2.5% keratin hydrolysate into hot-melt adhesive. As collagen is a natural polymer easy biodegradable in the aquatic environment, the research has focused on the possibility of its microbiological stabilization with aqueous solutions of ionic and colloidal silver. The highest microbiological activity was observed in a sample of ionic silver sulphate solution with a concentration of 2000 ppm Ag+. Its 1% concentration was applied for antibacterial thermoplastic stabilization of formaldehyde-free collagen glue.

Mechanical characterization and separation tests of a thermoplastic reinforced adhesive used for automotive applications

In the last decades, the use of structural and no structural adhesive has been increasing a lot in the automotive sector due to the advantages they can offer compared to traditional fasteners. Although they present many advantages, the impossibility to dismantle easily adhesive joints in order to substitute, recycle, reuse vehicle components or avoid waste for bonding errors is a factor that can limit their use. Furthermore, in Europe, the need to separate vehicle components for reuse and recycling is constrained by two Directives, 2000/53/EC and 2000/64/EC. These Directives set the objectives of reuse and recyclability for automotive vehicles, which are 95% and 85% respectively by an average weight per vehicle. For these reasons, it is very important to find a feasible solution to these problems. A promising technology for the separation of plastic joints, bonded with thermoplastic adhesives, uses nanomodified thermoplastic adhesives that are sensitive to electromagnetic fields. In this work, the mechanical behavior of adhesive joints made with a polyolefin adhesive, used in the automotive industry for bonding plastic components, have been studied. In particular, the adhesive has been modified with three different weight concentrations (3%, 5% and 10%) of iron oxide nanoparticles in order to make it sensitive to electromagnetic fields. These nanoparticles heat when are under the effect of an electromagnetic field and consequently they can melt the thermoplastic adhesive allowing for the joint separation. The mechanical properties of the joints prepared with the pristine and nanomodified particles have been studied by means of SLJ specimen with different overlap length and thicknesses. The adhesive joints prepared with the modified adhesives present a slightly higher load and a larger ductility compared to the ones prepared with the pristine one. Furthermore, separation tests have been performed in order to assess the times to disassemble these adhesive joints. Scanning electron microscope analysis has been used to assess the dispersion of the particles.

Automatic building of a web-like structure based on thermoplastic adhesive

Animals build structures to extend their control over certain aspects of the environment; e.g., orb-weaver spiders build webs to capture prey, etc. Inspired by this behaviour of animals, we attempt to develop robotics technology that allows a robot to automatically builds structures to help it accomplish certain tasks. In this paper we show automatic building of a web-like structure with a robot arm based on thermoplastic adhesive (TPA) material. The material properties of TPA, such as elasticity, adhesiveness, and low melting temperature, make it possible for a robot to form threads across an open space by an extrusion-drawing process and then combine several of these threads into a web-like structure. The problems addressed here are discovering which parameters determine the thickness of a thread and determining how web-like structures may be used for certain tasks. We first present a model for the extrusion and the drawing of TPA threads which also includes the temperature-dependent material properties. The model verification result shows that the increasing relative surface area of the TPA thread as it is drawn thinner increases the heat loss of the thread, and that by controlling how quickly the thread is drawn, a range of diameters can be achieved from 0.2–0.75 mm. We then present a method based on a generalized nonlinear finite element truss model. The model was validated and could predict the deformation of various web-like structures when payloads are added. At the end, we demonstrate automatic building of a web-like structure for payload bearing.

Large-Payload Climbing in Complex Vertical Environments Using Thermoplastic Adhesive Bonds

Despite many approaches proposed in the past, robotic climbing in a complex vertical environment is still a big challenge. We present here an alternative climbing technology that is based on thermoplastic adhesive (TPA) bonds. The approach has a great advantage because of its large payload capacity and viability to a wide range of flat surfaces and complex vertical terrains. The large payload capacity comes from a physical process of thermal bonding, while the wide applicability benefits from rheological properties of TPAs at higher temperatures and intermolecular forces between TPAs and adherends when being cooled down. A particular type of TPA has been used in combination with two robotic platforms, featuring different foot designs, including heating/cooling methods and construction of footpads. Various experiments have been conducted to quantitatively assess different aspects of the approach. Results show that an exceptionally high ratio of 500% between dynamic payloads and body mass can be achieved for stable and repeatable vertical climbing on flat surfaces at a low speed. Assessments on four types of typical complex vertical terrains with a measure, i.e., terrain shape index ranging from -0.114 to 0.167, return a universal success rate of 80%-100%.

Design Methods of Active Disassembly Structure Based on Thermoplastic Hot Melt Adhesive

Design Methods of Active Disassembly Structure Based on Thermoplastic Hot Melt Adhesive

Study on Properties and Preparation of Thermoplastic Polyurethane Hot-Melt Adhesive

The thermoplastic polyurethane elastomer (TPU) was firstly synthesized by using polybutylene adipate (PBA) as soft segments, methane-4-4’-diisocyanate(MDI) and 1,4–butanediol(BDO) as hard segments. The polyurethane hot-melt adhesive was then prepared by adding the tackifying resin, filler and other auxiliaries into the TPU matrix. The structure of the synthetic products was characterized by Infrared Spectrum and the thermal properties and microstructure of polyurethane hot-melt adhesive was tested by the thermogravimetric(TG) and the scanning electron microscopy(SEM), respectively. The results showed that the thermoplastic polyurethane elastomer had the expected structure, the shear strength of polyurethane hot-melt adhesive increased with the pentaerythritol abietate content increasing when the addition of the pentaerythritol abietate is less than 20 wt%, and decreased with the content of CaCO3 filler and petroleum resin increasing, respectively; the thermal stability was improved, and the char yields of the polyurethane blends increased with adding the filler CaCO3. When the molar ratio of PBA:MDI:BDO was 1:2:1, the addition of pentaerythritol abietate and filler CaCO3 was 20 wt% and 30 wt%, the comprehensive performance of PU hot-melt adhesive was better and the shear strength was 7.37 MPa.

Compatibility Improvement between Chlorinated Thermoplastic Rubber and Polychloroprene Adhesive

Abstract Traditionally, it has been believed that there is an incompatibility between the chlorinated rubber surface and polychloroprene adhesives resulting in a lack of adhesion. However, in this study it has been shown that a polychloroprene adhesive (PCP30P) produces similar T-peel strength values when using a polyurethane (PU) adhesive in joints produced between a chlorinated thermoplastic SBS rubber and roughened leather. In both cases a cohesive failure mode within the rubber was obtained. This polychloroprene adhesive (PCP30P) contains a thermoreactive phenolic resin in its formulation. The nature of the resin greatly influences the viscoelastic properties of the polychloroprene adhesive. Thus, polychloroprene adhesive with no resin or with resins of a different nature do not produce suitable adhesive joints between the chlorinated rubber and the leather (Terpene phenolic resin (PCP30TP), a glycerol esther colofony resin (PCP30EC) and an aromatic hydrocarbon resin (PCP30AH) were studied). The interactions produced between the chlorinating agent and the adhesive were studied by ATR-IR on solid films of the polychloroprene adhesives and the tackifier resins previously immersed in the chlorinating solution (0.5 and 3 wt% TCI/MEK). All the polychloroprene adhesives were modified by the chlorinating agent, being capable of producing a good interaction with the chlorinated rubber surface at the interface. Therefore, the good performance of the PCP30P adhesive compared with the other polychloroprene adhesives has been ascribed to rheological behavior more similar to the PU adhesive assessed by DMTA. The PCP30P adhesive is the most elastic material among all the considered polychloroprene adhesives. This increased elasticity and better viscoelastic properties are imparted by the thermoreactive phenolic resin in its formulation.

Pros and cons of thermoplastic and thermoset polymer adhesives in microelectronic assembly applications

Reviews the traditional use of thermoset (epoxy) adhesives for various bonding applications and highlights some limitations in today’s microelectronics arena. In particular, concerns for thermal and stress management associated with large area silicon bonded to a wide variety of substrate materials has led to an increasing interest in thermoplastic adhesive technology. Thermoplastics are not always the best solution for every application. This paper sets out to address the “pros and cons” of each polymer technology for different microelectronic applications taking into account some of the key physical properties such as Tg, TCE and modulus. In addition, practical issues such as handling, storage and processing are considered in detail.

New High Thermal Conductivity Thermoplastics for Power Applications

The trend towards higher density, higher frequency, higher power active devices in placing increasingly difficult demands on device packaging. Materials with high thermal conductivities are replacing the traditional ceramics in hermetic, high power packages, and MCM/ hybrid modules. Thermally enhanced plastic packages more frequently feature heat sinks embedded in the package for direct attachment of the power devices. Today's challenge in electronic packaging is to dissipate the heat from the source, the device itself, without affecting its electrical performance or reliability. The material directly contacting the device is the die attach medium. On lower power packages, the die bond line is not usually the highest thermal resistance in the thermal path. With highly conductive substrates and heat sinks, the die attach material now becomes the critical element directly in series with the highly conductive substrate. Fundamental limitations in thermal properties of about 3 W/mK exist in present‐day organic adhesives, primarily of the thermosetting type. This thermal conductivity (k) does not meet the current demands of thermally enhanced plastic laminate packages, MCMs, or direct die attach to heat spreaders or heat sinks. This paper describes the development, properties and application of electrically conductive thermoplastic adhesive pastes having thermal conductivity values as high as 35 W/mK, and able to produce thin, void‐free bond lines for maximum thermal transfer. The key material variables are isolated and evaluated for their impact of the k value. DOEs (design of experiments) were run to optimise the combination of the key variables, namely size/shape of the filler and the volume fraction to produce the highest k without sacrificing other functional properties such as adhesion. The effect of polymer chemistry (thermoset and thermoplastic) was also studied. The properties of the newly developed, enhanced conductivity thermoplastic adhesives are compared with other material technologies and examples of current applications reviewed.

Process‐induced effects in thin‐film bonding of PEKEKK in metal‐polymer joints

AbstractIn this work, poly ether ketone ether ketone ketone (PEKEKK) was used as a thermoplastic adhesive for joining metals. Titanium and cobalt chromium alloys were joined to form tensile butt joints. These tensile specimens were used to evaluate bond performance. A controlled thermal processing cycle was used to modify and enhance the polymer crystallinity during bonding. The resulting effects on bond performance were examined. The process window for a thermal bonding process was identified. Factorial experiments were conducted to determine the effects of modifications to adhesive and adherend material, and bonding pressure on bond performance. A titanium alloy and a cobalt chromium alloy were used as the adherends. Understanding changes in the thermoplastic adhesive joint with the variation of process parameters will allow for proper application and processing of thermoplastic structural adhesives.

The Effects of Molecular Weight on the Single Lap Shear Creep and Constant Strain Rate Behavior of Thermoplastic Polyimidesulfone Adhesive

The bonded shear creep and constant strain rate behaviors of zero, one, and three percent endcapped thermoplastic polyimidesulfone adhesive were examined at room and elevated temperatures. Endcapping was accomplished by the addition of phthalic anhydrides. The primary objective was to determine the effects of molecular weight on the mechanical properties of the adhesive. Viscoelastic and nonlinear elastic constitutive equations were utilized to model the adhesive. Ludwik's and Crochet's relations were used to describe the experimental failure data. The effects of molecular weight changes on the above mentioned mechanical behavior were assessed. The viscoelastic Chase-Goldsmith and elastic nonlinear relations gave a good fit to the experimental stress strain behavior. Crochet's relations based on Maxwell and Chase-Goldsmith models were fit to delayed failure data. Ludwik's equations revealed negligible rate dependence. Ultimate stress levels and the safe levels for creep stresses were found to decrease as molecular weight was reduced.